The vaginal mucosa (VM) is one of the critical interfaces between host and pathogens. Normally, it can tolerate and contain a broad range of microbes and cope with foreign proteins including those present in the ejaculate. Hence, VM is likely to be equipped with an arsenal of defenses similar to that of the other such mucosal interfaces, e.g., lung and gut. This proposal focuses on vaginitis, a condition resulting from a breakdown of defenses against organisms that remain largely localized yet can have major consequences for the host and her reproductive capacity. Vaginitis is responsible for up to 15% of patient visits to women's health practices. The sequelae of VM have great effects on public health, and are implicated in disorders ranging from preterm labor and associated morbidity and mortality of the offspring, to increased susceptibility to sexually transmitted disease and progression of cervical neoplasia. Yet, knowledge of vaginal host defenses has lagged behind that of other mucosal surfaces. Here we propose to follow up on evidence obtained by us that SP-A is expressed in VM and is present in VF by testing the hypotheses that: (1) SP-A in VF, as in lung, contributes to host defenses by modulating cytokine production and facilitating phagocytosis; (2) SP-A expression in VM and function in VF, like other mediators of vaginal immunity, vary with menstrual cycle (i.e., is hormonally regulated); and (3) aberrant SP-A homeostasis contributes to recurrent vulvovaginal candidiasis (RVVC), a prevalent, intractable condition of women of reproductive age that is characterized by episodes of exacerbations of inflammation of the VM due to colonization of the vagina with C. albicans. Parameters relevant to SP-A function will be compared: (1) in healthy women at three stages of the menstrual cycle; (2) in healthy women and RVVC patients; and (3) in RVVC patients during remissions and exacerbations of the disease. In VM, SP-A will be localized by immunocytochemistry and gene-specific message levels will be estimated by reverse transcriptase/polymerase chain reaction (RT/PCR). In VF, SP-A levels will be measured by enzyme-linked immunoabsorbent assay (ELISA), SP-A oligomeric size established by gel filtration and ability of SP-A to stimulate production of proximal cytokines and to facilitate phagocytosis. This will be accomplished using THP-1 macrophages adapted to grow as surrogates for vaginal macrophages in a medium that simulates VF fluid with respect to certain determinants of SP-A function, such as pH, electrolyte and cation concentrations. Immunodepletion will be used to determine the contribution made by SP-A to stimulation of cytokine production by TPH-1 cells.